Beryllium-aluminum composite



y 22, 1969 R. H. KROCK ET M BERYLLIUM-ALUMINUM COMPOSITE Original Filed March 10, 1966 2 Sheets-Sheet l ALUMINUM- BERYLLIUM PHASE DIAGRAM WEIGHT PER cam BERYLLIUM 5 IO I5 BO 5O 6O 70 809 l l l l J l l 1 TEMPERATURE, C

AM- Re I0 20 30 Q0 BO 8O I00 ATOMIC PER CENT BERYLLIUM mvzrvrons RICHARD H. KROCK gumroao R. JONES July 22, 1969 R. H. KROCK ET AL 3,456,322

BERYLLIUM-ALUMINUM COMPOS ITE Original Filed March 10, 1966 2 Sheets-Shee t 2 INVENTORS RICHARD H. KROCK CLINTFORD R. JONES 3,456,322 BERYLLIUM-ALUMINUM CGMPOSITE Richard H. Krock, Peabody, and Clintford R. Jones,

Arlington, Mass., assignors to P. R. Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware Original application Mar. 10, 1966, Ser. No. 533,156. Divided and this application Aug. 14, 1967, Ser. No. 671,176

Int. Cl. B22f 7/00 U.S. Cl. 29182.1 7 Claims ABSTRACT OF THE DISCLOSURE A metal composite consisting essentially of 50-90% by weight beryllium, the remainder aluminum.

This is a division of application Ser. No. 533,156, filed Mar. 10, 1966, and now abandoned.

The present invention relates to prime composites of beryllium-aluminum and more particularly to means and methods for providing such composites through liquid phase sintering.

Liquid phase sintering differs from the several other types of sintering techniques in that the sintering of the compact is carried out in the presence of a liquid phase. Liquid phase sintering encompasses raising the temperature of the compressed powder metal consituents to a temperature wherein a predetermined amount of the liquid phase appears. In the liquid phase, one of the metal constituents, the solid, is progressively dissolved in the other metal constituent, the liquid. However, the quantities of these constituents are such that, at equilibrium, some solid phase always exists. It is thought that the liquid wets the solid so as to bring about favorable surface energies existing between the liquid and the solid thereby permitting solution into the liquid phase.

However, heretofore, when beryllium-aluminum composites were developed in accordance with known liquid phase sintering techniques, it was found that the solid, beryllium, expelled the liquid, aluminum-beryllium alloy from the compact during liquid phase sintering. It is thought that the unfavorable surface energy equilibrium causing expulsion of the liquid is due to a tough, tenacious film of beryllium oxide which is present on each particle of beryllium.

The present invention prevents the expulsion of the liquid from the specimen by using an agency to intervene in the sintering stage. The agency either breaks down the oxide film on the beryllium or segregates to the metal oxide interface and lowers the surface energy of the liquid metal with respect to the beryllium oxide film so that the liquid metal progressively dissolves the solid metal.

The agency can be called a fluxing agent or flux, however, the agent has other characteristics which assist in wetting beryllium so as to surround the beryllium with a ductile envelope phase of an aluminum-beryllium alloy matrix metal thereby avoiding the expulsion of the liquid from the specimen.

Beryllium has several desirable physical features which make it attractive for a variety of application such as lightweight gears, lightweight fasteners, airplane parts or the like. Beryllium metal is lighter than aluminum metal and has a melting temperature that is about twice that of aluminum. However, beryllium has one major drawback which has seriously limited its commercial acceptance, that is, beryllium is inherently brittle at room temperature.

The lack of ductility of beryllium is attributed to the crystal structure of beryllium which is hexagonal close packed. During deformation, the basal planes of the hex- 3,456,322 Patented July 22, 1969 ice agonal close packed structure, being the easiest to slip, are aligned along the working direction. Since slip is crystallographically difiicult perpendicular to the basal plane, the ductility of beryllium perpendicular to the primary fabrication direction is practically nonexistent.

Several tentative solutions have been advanced in an attempt ot make beryllium metal sufiiciently ductile so as to permit a widespread commercial acceptance of the metal. Cross-rolling and cross-forging have been suggested as fabrication methods which might enhance the ductility of beryllium. These fabrication techniques reduced the number of basal planes along the direction of rolling and resulted in improved ductility. However, the degree of improvement was far from satisfactory. The fact remained that beryllium must be classified as brittle at room temperature even utilizing the aforementioned method when ductility perpendicular to the fabrication temperature is considered. In addition, the above mentioned technique would not be feasible where the fabrication is, by nature, solely along one axis such as swaging, drawing, and extrusion.

In recent years, attention has been directed to the fabrication of beryllium alloys not having the inherent brittleness of beryllium itself but possessing various outstanding properties of the metal such as, for example, low density combined with high strength. It is thought that U.S. Patent 3,082,521 fabricated the first ductile beryllium alloy by rapidly quenching the part from a temperature at which it was liquid. However, the beryllium content was not in excess of 86.3 atomic percent which is approximately 30 weight percent. Although the beryllium alloy was ductile, the density of the alloy was in excess of that of aluminum and about equal to that of titanium.

It has also been suggested that beryllium alloys might be fabricated by pressing and sintering a mix of metal powders. However, such a method results in expulsion of the matrix metal or metals from the beryllium specimen and the eventual freezing of the matrix metal or metals into globs on the surface of the solid specimen. It is thought that the expulsion of the matrix metal or metals is due to the surface energies of the solid beryllium and the various liquids formed. The unfavorable surface energy equilibrium is believed to be due to a tough, tenacious film of beryllium oxide which is present on each particle of beryllium.

A means and method have been discovered for preparing a composite of beryllium and aluminum containing from about 50' to percent, by weight, of beryllium thereby producing a composite having a density less than that of aluminum, having high strength, and having good ductility. The ductility is due to the resulting microstructure of the composite. By surrounding the beryllium particles with a ductile envelope phase, a composite is formed where, under load, the beryllium is so constrained by the ductile phase that it and the ductile phase deform continuously.

Alkali and alkaline earth halogenide agents such as lithium fluoride-lithium chloride or the like in a determined ratio are utilized to segregate to the solid interface of the beryllium particle and either break down the film on the particle of beryllium and/ or alter the liquid-solid surface energy in the system.

Therefore, it is an object of the present invention to provide an agent to promote liquid phase sintering of a beryllium-aluminum mixture.

A further object of the present invention is to provide a ductile beryllium composite having a low density and high strength.

A further object of the present invention is to provide a ductile composite of beryllium in which beryllium is the predominant ingredient.

Another object of the present invention is to provide a means and method of producing a ductile composite of beryllium-aluminum whose microstructure consists of beryllium particles surrounded by a ductile envelope phase of an aluminum-beryllium alloy matrix metal, or by a ductile envelope phase of essentially pure aluminum.

Yet another object of the present invention is to provide a ductile composite of beryllium containing 50 percent, by weight, or more of beryllium.

Yet another object of the present invention is to provide a ductile composite of beryllium-aluminum containing about 70 percent, by weight, beryllium, and the remainder aluminum.

A further object of the present invention is to provide an agent which eliminates the expulsion of a matrix metal from a beryllium specimen.

Still another object of the present invention is to provide alkali and alkaline earth halogenide agents used in the fabrication of a beryllium composite.

Another object of the present invention is to provide a composite of beryllium-aluminum that may be sintered to substantially theoretical density.

Yet another object of the present invention is to provide a means and method whereby a ductile beryllium composite may be successfully fabricated in both a practical and economical manner.

A further object of the present invention is to provide a lithium fluoride-lithium chloride agent for promoting liquid phase sintering in a beryllium and aluminum mix.

Yet still another object of the present invention is to provide a lithium fluoride-lithium chloride agent wherein the constituents are are used in a predetermined ratio.

The present invention, in another of its aspects, relates to novel features of the instrumentalities of the invention described herein for teaching the principal object of the invention and to the novel principles employed in the instrumentalities whether or not these features and principles may be used in the said object and/or in the said field.

With the aforementioned objects enumerated, other objects will be apparent to those persons possessing ordinary skill in the art. Other objects will appear in the following description and appended claims. The invention resides in the novel combination of elements and in the means and method of achieving the combination as hereinafter described and more particularly as defined in the appended claims.

In the drawings:

FIGURE 1 is a phase diagram for binary alloys of beryllium and aluminum.

FIGURE 2 is a photomicrograph of a beryllium specimen illustrating a matrix metal expelled from the specimen by the forces of surf-ace energy of solid beryllium and various liquids formed.

FIGURE 3 is a photomicrograph of a 30 percent, by weight, aluminum in beryllium composite illustrating the structure of said composite after sintering at 1000 centigrade for 1 hour.

FIGURE 4 is a photomicrograph of a 30 percent, by weight, aluminum in beryllium composite illustrating the structure of said composite after two represses at 40,000 p.s.i. each followed by an intermediate sinter at 1000 centigrade.

Generally speaking, the means and method of the present invention relate to a ductile beryllium composite fabricated by liquid phase sintering. The composite contains from about 50 to 90 percent, by weight, of beryllium, and the remainder aluminum.

The method of producing the beryllium-aluminum composite by liquid phase sintering comprises the steps of mixing predetermined portions of powder beryllium and powder aluminum together with a predetermined portion of an agent selected from the group consisting of alkali and alkaline earth halogenides. The portions are pressed in a die to form a green compact. The compact is then v heated to the sintering temperature. At this temperature the agent provides a favorable surface energy equilibrium between the beryllium land the aluminum so that the aluminum progressively dissolves the beryllium at the sintering temperature. Thereafter, the composite may be quenched so as to substantially preserve the phase relations that existed at the sintering temperature. Equilibrium cooling results in a beryllium mix of a duplex microstructure at room temperature consisting of solid beryllium particles dispersed in a matrix of pure aluminum.

More particularly, the method of the present invention comprises mixing powder beryllium of about 50 to percent, by weight, and the remainder powder aluminum. An agent of lithium fluoride-lithium chloride in about 0.5 to 1.0 percent, by weight, of the total metal additions is mixed with the beryllium and the aluminum powders. The constituents of the agent are in about a one to one ratio, by weight. The beryllium, the aluminum, and the agent are pressed so as toform a green compact. The green compact is heated in a non-oxidizing atmosphere such as argon at a temperature of about 800 centigrade to about 1100 centigrade. At the aforementioned temperatures, the agent provides a favorable surface energy equilibrium between the beryllium and the aluminum so that the aluminum progressively dissolves the beryllium. The microstructure of the composite consists of beryllium particles surrounded by a ductile envelope phase of an aluminum-beryllium alloy matrix metal. The composite is sintered to substantially its theoretical density. If the composite is quenched from the sintering temperature, the phase relation at the sintering temperature is preserved, that is, the resultant composite consists of beryllium particles surrounded by an aluminum-beryllium matrix alloy. Equilibrium cooling results in a duplex microstructure at room temperature of solid beryllium particles dispersed in a matrix of pure aluminum.

In carrying out the present invention, a beryllium base compact is fabricated by any suitable means such as powder metallurgy techniques. A suggested method utilizing this technique is to mix beryllium powder with powdered aluminum and an agent of equal parts of lithium fluoridelithium chloride. The powders are blended and mixed by ball milling the metal powders and the flux agent. The blended and mixed powders are compacted to form a green compact by accepted metallurgical methods such as by compacting within the confines of a die or a hydraulic or an automatic press or by placing the powders in a rubber or a plastic mold and compacting in a hydrostatic press. The green compact is sintered in a nonoxidizing atmosphere such as argon or the like at a temperature of about 800 centigrade to about ll00 centigrade. It is seen that the range of the sintering temperatures is below the 1277 centigrade melting point temperature of beryllium but above the 660 centigrade melting point temperature of aluminum. The aluminum will dissolve smaller beryllium perticles and will dissolve the surfaces of the larger beryllium powder particles thereby surrounding the remaining beryllium particles with a ductile envelope phase of an aluminum-beryllium alloy during sintering of the compact.

The agent, lithium fluoride-lithium chloride, either breaks down the oxide film on the beryllium or segregates to the metal oxide interface lowering the surface energy of the liquid metal with respect to the beryllium oxide film. Simply, the agent causes the liquid to wet the beryllium.

Composites containing about 50 to 90 percent, by Weight, of beryllium, and the remainder aluminum were successfully fabricated. The agent prevented the expulsion of the liquid aluminum-beryllium alloy from the compact by the forces of surface energy, that is, prevented the formation of very fine rounded droplets of the aluminumberyllium alloy on the surface of the beryllium specimen. FIGURE 2 shows a beryllium specimen 20 having on the surface thereof an expelled alloy 21 of aluminum-beryllium. Specimens from which the a1uminum-beryllium aly has been expelled have gross porosity and as a result are weak, brittle, and of little commercial value.

The composition of the agent utilized is about 50 parts, by weight, of lithium fluoride to about 50 parts, by weight, of lithium chloride. The agent provides an action, such that, upon heating or sintering of the pressed powder mix to the temperature at which the liquid phase forms, eX- pulsion of the melt from the specimen is eliminated. Furthermore, it was found that solution of the beryllium into the aluminum was enhanced as evidenced by the rounded particles of beryllium in the microstructure.

It was found that the amount by weight of lithium fluoride-lithium chloride agent should exceed 0.5 percent, by weight, of the total of all metal additions. 'It would appear that the optimum range of the agent is from about 0.5 percent to about 1.0 percent, by weight, of the total of all metal additions. It is believed that the quantity of lithium fluoride-lithium chloride agent required is related to the amount necessary to cover the total beryllium surface area. Hence, the minimum amount of agent needed would be a function of the surface area of the beryllium powder. The utilization of lithium fluoridelithium chloride agent in other than equal parts or in amounts greater than 1.0 percent by weight of all the metal additions is possible. It is thought, however, that an equal parts mixture and 0.5 to 1.0 percent by weight of all the metal additions achieves optimum results.

By using the methods of the present invention and the lithium fluoride-lithium chloride agent, composites were fabricated containing from about 50 to 90 percent, by weight, of beryllium without the use of pressure during sintering. The composites were sintered to between about 76.5 and 89 percent of their theoretical density by a single sinter and 96 percent of theoretical density by a double repress and an intermediate re-liquid phase sinter and had a density of about 1.94 grams per cubic centimeter. The good strength and low density characteristics of the beryllium were retained and the resulting beryllium aluminum composites possessed good ductility. Thus, by substantially surrounding the beryllium particles with a ductile envelope phase of an aluminum-beryllium alloy matrix metal or a ductile envelope phaseof essentially pure aluminum matrix metal, the beryllium and the matrix metal deform continuously under load.

The beryllium-aluminum phase diagram of FIGURE 1 illustrates that when a beryllium-aluminum mixture containing 70 perecent, by weight, beryllium and 30 percent, by weight, aluminum is heated, a liquid forms at 645 centigrade containing 1%. weight percent beryllium, balance aluminum in equilibrium with solid beryllium. Sintering at a higher temperature results in solid beryllium in equilibrium with a liquid richer in beryllium. For example, at 800 centigrade the liquid Would contain about 2 /2 percent, by weight, beryllium, at 1000 centigrade about 9 percent, by weight, beryllium, and at 1100 centigrade about 20 percent, by weight, beryllium. Hence, for a 70 percent, by weight, beryllium mixture, the volume percent liquid present at the sintering temperature and the composition of the liquid is a function of the sintering temperature. Very rapid cooling, such as, for example, quenching, from the sintering temperature would preserve the phase relations that existed at the sintering temperature while equilibrium cooling results in a 70 percent, by weight, beryllium mix of a duplex microstructure at room temperature consisting of 70 percent, by weight, beryllium as solid beryllium particles dispersed in a matrix of 30 percent, by weight, pure aluminum. The volume percentages of liquid and solid present at the sintering temperatures of 800, 1000 and 1l00 centigrade for various beryllium and aluminum mixtures are given in the following table.

PHASE RELATIONSHIPS IN A BERYLLIUM-ALUMINUM SYSTEM Percent; Percent Percent sintering by y y Composite Temperature, Initial Weight Volume Volume Density 0. Composition Liquid Liquid Liquid grns./ce,

800 50 Be-50 AL 51. 3 41. 0 59. 0 2. 18 60 Be-40 A1. 41.0 30. 5 69. 5 2.09 70 B6-30 AL 30. 8 22. 5 77. 5 2. 02 Be-20 AL 20. 5 13. 5 86. 5 1. 04 Be-lO Al- 10. 2 7.0 93.0 1. 88

1,000 50 Be-50 Al- 54. 5 45.0 55.0 2.18 60 Be-40 Al- 43. 5 34. 0 66. 0 2.09 70 Be-30 Al- 32. 6 25. 0 75. 0 2. 02 80 Be-20 AL 21. 7 15. 0 85. 0 1. 94 90 Be-lO Al. 10. 9 7. 5 92.5 1. 88

1,100 50 Be-50 AL 62.5 56.0 44. 0 2. 18 60 Be-40 A1. 50.0 42.0 58.0 2.09 70 Be-30 Al- 37. 6 31.0 69.0 2.02 80 Be-20 Al- 25.0 19.0 81.0 1. 94 90 Be-lO Al. 12. 5 9.0 91. 0 1. 88

It will be noted that the density values of the composites fall between the density of beryllium and the density of aluminum. The resulting composite containing from about 70 percent, by weight, of beryllium may be sintered to about 76.5 percent of density by a single sinter. Composites containing about 70 percent, by weight, of beryllium require a double repress at 40,000 pounds per square inch and an intermediate re-liquid phase sinter at 1000 centigrade to attain about 96 percent of theoretical density.

Attention is directed to FIGURE 3, wherein a photomicrograph of 500 magnifications shows an alloy of 30 percent, by weight aluminum in beryllium composite after being etched by any suitable etching means such as a dilute solution of ammonium hydroxide and hydrogen peroxide. The areas 10 are sintered beryllium particles. The area 11 is the ductile pure aluminum matrix which surrounds the beryllium particles. The compact was sintered for 1 hour in an argon atmosphere at 1000 C. and had a density of about 1.80 grams per cubic centimeter which was about 89% of the theoretical density.

FIGURE 4 shows the structure of an alloy of 30 percent, by weight, aluminum in beryllium composite that has been subjected to two represses at about 40,000 psi. followed by an intermediate sinter at 1000 centigrade. The density is about 1.94 grams per cubic centimeter which is approximately 95.2% of the theoretical density.

Example 1 shows the expulsion of the liquid from a beryllium specimen and Examples 2 to 6 are illustrative of the preparation of beryllium-aluminum composites by liquid phase sintering.

EXAMPLE 1 Expulsion of the liquid aluminum-beryllium alloy from the solid beryllium specimen when the agent of lithium fluoride-lithium chloride is not used in the preparation of a beryllium-aluminum composite.

A mixture of about 70 percent, by weight, of beryllium having a particle size of 200 mesh or finer was ball mill mixed with about 30 percent, by weight, of aluminum powder of suitable particle size. The milled mixture was pressed by any suitable means such as by an automatic press at a suitable pressure to provide a green compact sturdy enough to be handled. It was found that pressures of from about 15,000 to 20,000 pounds per square inch resulted in a green compact having a density from about 50 to 60 percent of theoretical density and sufliciently strong to be handled. Sintering of the compact was carried out in an argon atmosphere at about 1000 centigrade for about 1 hour. This technique, due to the surface energies of the solid beryllium and the liquid formed, resulted in the expulsion of the liquid from the specimen and its eventual freezing into rounded globs on the surface of the specimen.

EXAMPLE 2.

A composite of about 70 percent, by weight, beryllium and about 30 percent, by weight, of aluminum.

A mixture of about 70 percent, by weight, of beryllium having a particle size of about 200 mesh or finer was ball mill mixed with about 30 percent, by weight, of aluminum powder of suitable particle size. Also ball mill mixed with the beryllium powder and the aluminum powder was about 1.0 percent, by weight, of the total metal additions of equal parts of a flux agent of lithium fluoride-lithium chloride. A mixture of beryllium powder and aluminum powder was also prepared the lithium fluoride-lithium chloride agent having 0.5 percent, by weight, of the total metal additions. The milled mixture was pressed by any suitable means such as by an automatic press at a suitable pressure to provide a green compact sturdy enough to be handled. It was found that pressures of from about 15,000 to 20,000 pounds per square inch resulted in a green compact having a density of from about 50 to 60 percent of theoretical density and sufficiently strong to be handled. Sintering of the compact was carried out in an argon atmosphere at about 1000 centigrade for about 1 hour. The composition was then subjected to two represses followed by an intermediate sinter at 1000 for about one to two hours. An individual composite was prepared using the above mentioned procedure at each of the hereinafter enumerated temperatures of 800 and 11 centigrade. Each of the composites was allowed to undergo equilibrium cooling to form a composite of beryllium particles dispersed in a matrix of pure aluminum. The overall composition was 70 parts, by weight, beryllium, and 30 parts, by weight, aluminum.

EXAMPLE 3 A composite of about 50 percent, by weight, beryllium and about 50 percent, by weight, aluminum.

The procedure of Example 2 was followed using 50 percent, by weight, of beryllium and 50 percent, by weight, of aluminum. An individual composite was prepared at each of the following temperatures of about 800, 1000 and 1100 centigrade using the aforementioned procedure.

EXAMPLE 4 A composite of about 60 percent, by weight, beryllium and about 40 percent, by weight, aluminum.

The procedure of Example 2 was followed using about 60 percent, by weight, of beryllium and about 40 percent, by weight, of aluminum. An individual composite was prepared and heated to one of the following temperatures of about 800, 1000 and ll00 centigrade.

EXAMPLE 5 A composite of about 80 percent, by weight, beryllium and about 20 percent, by weight, aluminum.

The procedure of Example 2 was followed using about 80 percent, by weight, of beryllium and about 20 percent, by weight, of aluminum. An individual composite was prepared and heated to one of the following temperatures of about 800", 1000 and 1100" centigrade.

EXAMPLE "6 A composite about 90 percent, by weight, beryllium and about 10 percent, by weight, aluminum.

The procedure of Example 2 was followed using 90 percent, by weight, of beryllium and 10 percent, by weight, of aluminum. An individual composite was prepared at each of the following temperatures of about 800, 1000 and 1100 centigrade using the aforementioned procedure.

The present invention is not intended to be limited to the disclosure herein, and changes and modifications may be made in the disclosure without departing from the scope of the novel concepts of this invention and as set forth in the appended claims.

Having thus described our invention, we claim:

1. A metal composite consisting essentially of about 50 to about 90 weight percent beryllium, the remainder aluminum, said beryllium being substantially round particles substantially surrounded by a matrix consisting essentially of aluminum.

2. The metal composite of claim 1, wherein said beryllium is about weight percent, the remainder said aluminum.

3. The metal composite of claim 1, wherein said composite has a density up to about 95 percent of theoretical density.

4. The metal composite of claim 1, wherein said matrix consists essentially of aluminum and up to about 20 weight percent beryllium.

5. The metal composite of claim 4, wherein said matrix consists essentially of aluminum and up to about 9 weight percent beryllium.

6. The metal composite of claim 5, wherein said beryllium is about 70 weight percent, the remainder said aluminum.

7. The metal composite of claim 6, wherein said metal composite has a density up to about 95 percent of theoretical density.

References Cited UNITED STATES PATENTS 2,072,067 2/1937 Donahue -150 3,378,356 4/1968 Larsen et al. 29-182.1 3,337,334 8/1967 Fenn et a1. 75-150 CARL D. QUARFORTH, Primary Examiner ARTHUR I. STE'lIN-ER, Assistant Examiner 

